Overload relief assembly for power presses



y 4, 195.0 J. c. DANLY 2,937,733

OVERLOAD RELIEF ASSEMBLY FOR POWER PRESSES Filed Oct. 31, 1956 3Sheets-Sheet 1 III/11m INVENTOR JZJMES C. DAM/1V A ORNEY May 24, 1960OVERLOAD RELIEF ASSEMBLY FOR PCWER PRES-3E5 Filed Oct. 31, 1956 3Sheets-Sheet 2 INVENTOR .72/0155 6 014M) A ORNEY J. c. DAN-LY 2,937,733

y 24, 1960 J. c. DANLY 2,937,733,

OVERLOAD RELIEF ASSEMBLY FOR POWER PRESSES Filgjad Oct. 31, 1956 5Sheets-Sheet 3 mm "In INVENTOR 72/4455 C. pfiA/LY OVERLOAD RELIEFASSEMBLY FOR POWER PRESSES My invention relates to an overload reliefassembly for power presses having-one or more connections to the pressworking slide and more particularly to an overload relief assembly whichrelieves an overload occurring on one or more of the corners of theworking slide either by relieving the load on the slide connections orby relieving the load on the press tie rods.

Overdrive presses are assembled with tie rods which are placed under aheavy predetermined tension. In operation of the press, if for anyreason the press is overloaded, extreme damagesuch as bending of aneccentric shaft or rupturing or straining of the press tie rods islikely to result.

Patent No. 2,616,543, issued to Philo H. Danly on November 4, 1952,discloses a safety assembly for power presses which stops the press inthe event of an overload on any one of the press tie rods. In the systemdisclosed in the said patent, fluid under pressure is fed to press tierod cylinders carried by the press frame. This fluid acts on pistonscarried by the tie rods to place the rods under the proper predeterminedtension; When an overload occurs on a particular rod, the piston isdisplaced to relieve the tension on this rod and to stop the ress.

p One case in which a press is overloaded occurs when material of athickness greater than the material thickness for which the press is setis fed into the press. If this increased thickness is uniform throughoutthe material, the system of the patent referred to hereinabove operatessatisfactorily to relieve the increased tie rod tension and to stop thepress. If, however, the material being fed to the press is not uniformlythicker with the result that not all the tie rods are placed underincreased tension, the tension on only those rods which are overloadedis relieved. In the system described in the said patent, in the-eventsuch an unsymmetrical overload occurs, tension on all rods may be, butis not necessarily, equalized. It often happens that one rod ispermitted to give in response to an unsymmetrical overload, but theother rods do not give since the fluid pressure to these rods ismomentarily increased when the one rod is overloaded. It will beappreciated that if one or more rods, but not all rods, give, theresulting forces tend to cockbill the press slide with resulting damageto press parts, such as the gibs.

In a first form of my invention I have provided an overload relief,assembly for power presses which embodies an improvement on the safetyassembly disclosed in the said patent. My system ensures that if any oneof the press tie rods is overloaded, the tension on all the rods -willbe relieved. My system includes means for stopping the press in theevent of an unsymmetrical overload. My assembly relieves tension on allthe press tie rods in response to an unsymmetrical overload to preventdamage to -press parts such as thedrawing slide gibs.

-. In single action presses, a tie rod overload relief mechaeffectivelyrelieves the overload applied to the press slide. In the case ofoverdrive multiple point suspension United States Patent result a reliefsystem applied to these heavily loaded tie rods will not be suflicientlysensitive to respond to an overload on the relatively lightly loadedblank holder.

In a second form of my invention, I have provided an overload reliefassembly which may be applied either to the press inner slide drivingconnections orto the press blank holder driving connections. In eithercase this sys tem operates to relieve an overload imposed on the slideto which the system has been applied. As is the case with my tie rodoverload relief system, overloading of any one of the drivingconnections of a slide results in relieving the load on the remainingslide connections in the event an unsymmetrical loading occurs.

One object of my invention is to provide an improved overload reliefassembly for power presses which relieves the tension on all the presstie rods when any one of the rods is overloaded.

Another object of my invention is to provide an improved overloadreliefassembly for power presses which may be applied directly to theslides of the press.

Still another object of my invention is to provide an improved overloadrelief assembly for power presses which stops the press operation inresponse to an unsymmetrical overload.

A still further object of my invention is to provide an improvedoverload relief assembly for power presses which maintains constant theforce acting on the press tie rods.

which prevents damage to the press in the event a sheet of stock ofirregular thickness is fed to the press.

Other and further objects of my invention will appear from the followingdescription:

In general the first embodiment of my invention contemplates theprovision of an overload relief assembly for power presses in which aplurality of press tie rods carry pistons which are associated withcylinders to which fluid under a predetermined pressure is fed from acommon source through respective valve assemblies. If, owing to anunsymmetrical overload being applied to the press, the tension on anyone of the rods exceeds the tension corresponding to said predeterminedpressure, the associated piston drives fluid back into its valveassembly to actuate the valve to relieve the fluid pressure. Theconstruction and arrangement of the valve assemblies is such thatactuation of any one of the valve assemblies relieves the pressurethroughout the system to permit the other tie rod pistons to actuatetheir respective valves to relieve tension on all the rods. Meansresponsive to operation of any of the valve assemblies is adapted tostop the press.

The second embodiment of my invention contemplates the provision of anoverload relief assembly for a multiple point suspension power pressincluding a respective hydraulic cylinder and piston coupling each ofthe slide.

drive members to the slide. Fluid under a predetermined pressure is fedfrom a common source to respective valve assemblies connected to thecylinders. Upon the occurrence of an overload, the system of this secondembodiment operates in the same manner as the tie rod relief assemblydescribed above to relieve the pressure throughconjunction therewith andin which like reference numerals are used to indicate like parts in thevarious views:

Figure 1 is a perspective view of a power press provided with myoverload relief assembly with parts of the press broken away.

Figure 2 is a schematic view of the first form of my overload reliefassembly for power presses.

Figure 3 is a sectional view of one of the tie rod. cylinder supplyvalve assemblies of my overload relief assembly for power presses.

Figure 4 is a fragmentary sectional view of the second embodiment of myoverload relief assembly for power presses.

More particularly referring now to Figure 1 of the drawings, a powerpress, indicated generally by the reference character 10, is assembledwith a plurality of respective tie rods 12, 1-4, 16, and 18. These tierods hold the press 10 assemblied under a predetermined tension. Thepress 10 includes a slide 20 which reciprocates toward and away from thepress bed 22.

Referring now. to Figure 2, each of the respective rods 12, 14, 16, and18 carries a piston 24 held against an annular shoulder 26 on the rod bymeans of a nut 28 threaded on the rod end. Each of a plurality ofrespective cylinders 30 associated with pistons 24 is supplied withfluid under pressure from one of a plurality of respective supply valveassemblies, indicated generally by the reference characters 32, 34, 36,and 38. The cylinders 3 are carried by or formed in the framev of press10.

Referring now to Figures 2 and, 3, each of, the valvev assemblies 32,34, 36, and 38 has a body 40 formedwith a bore 42. As shownschematically in Figure 2, a pipe 44 connects an opening in a first endplate 46 secured to the body 40 by any convenient means to an openingformed in the wall of the cylinder 30 with which the particular valveassembly 32, 34, 36, or 38 is associated. It will be appreciated thatthe, pipes 44 provide communication between the, respective bores 42 andthe interiors of cylinders 30. As is indicated in Figure 3, in theactual construction of my assembly, the valve body of 40 may be securedto the wall of the associated cylinder 30 by means such as welding orthe like with bore 42 communicating directly with the interior of thecylinder. I dispose a piston 48 provided with a bore 50, one end ofwhich is closed by the piston head 52, within the bore 42 of the valvebody. Springs 54 bear between heads 52 and end plates 56, which aresecured to bodies,

40 by any convenient means such as bolts 58, to urge the pistons 48 tothe left as viewed in Figure 2. One edge of an annular enlargement 60formed in bore 42 provides a seat 53 for head 52. A bore 62 in the wallof body 40 communicates with the enlargement 60 to permit any fluid inthis enlargement to pass out of the valve and into a relief pipe 64.

A fitting 66 connects a supply pipe 68 to an opening 70 in wall 56,which opening leads into bore 42. I provide the wall of piston 48 withopenings 72 communicating with a second annular enlargement 74 in bore42. A passage 76 in the wall of body 40 bypasses enlargement 60 topermit fluid to flow from the enlargement 74 into the portion of bore 42to the left of seat 53 as viewed in Figure 3. I dispose a cheek valve,including a ball 78 urged against a seat 80 by a spring 82, in passage76. For purposes of clarity the passages 76 are shown as ex-. ternalpipes 84 in Figure 2. valves including balls 78, are indicatedschematically by the reference characters, 86. V

In a normal condition of any one of my valve assentblies 32, 34, 36, or3,8, itsspring 54 urges piston 48 to the left as viewed in Figures 2 and3, to urge head 2 against seat 53, Fluid under pressure fed into bore.42 passes through openings72 into enlargement 74, through passage 76,past ball 78 and into the portion of bore 42 to the left of seat 53. histo be understoodthat in this condition of' a valve, the wall of piston48 engages the In this figure, they check,

portion of the wall of body 40 separating enlargements and 74 to form avalve which prevents entry of fluid into enlargement 60. If, as will beexplained hereinafter, the pressure in the portion of bore 42 to theleft of seat 53 increases to urge head 52 to the right as viewed inFigures 2 and 3 against the action of spring 54, the piston 48 moves topermit communication between enlargements 60 and 74 to allow fluid beingfed to the valve to be relieved through pipe 64.

T-fitting 88 connects the supply pipes 68 leading to the respectivevalve assemblies 36 and 38 to a pipe 90. A fitting 92 connects pipe andthe pipes 68 leading to the respective valve assemblies 32 and 34 to themain supply pipe 94. My hydraulic system includes a pump 96, the shaft98 of which is driven by a motor 100. A pipe 102 connects the inlet ofpump 96 to a source (not shown) of fluid such as oil. A check valve 104connects the outlet side of pump 96 to a relief valve 106 connected tothe main supply pipe 94. Check valve 104 permits fluid to be pumped intothe system but prevents oil from returning to the pump. Relief valve 106permits fluid to flow out of the system through a pipe 108 if the fluidpressure exceeds a predetermined value. A valve 110 connected to line 94may be actuated to permit fluid to enter a pressure meter 112.

My system includes an accumulator, indicated generally' by the referencecharacter 114, which maintains the oil in the system at a predeterminedpressure corresponding to the required tie rod tension. Accumulator 114is made up of a first cylinder 116 and a second cylinder 118. Respectivepistons 120 and 122 move together and cooperate with the respectivecylinders 116' and 118. A pipe 124 communicates with the interior ofcylinder 116 to supply air under pressure to the cylinder below thepiston 120. A pipe 126 connects the interior of cylinder 118 over piston122 to supply pipe 94 to permit oil to enter cylinder 118. A pump 126,the inlet side of which is connected to the atmosphere by a pipe 128,supplies compressed air to an outlet pipe 130. A motor 132 drives theshaft 134 of pump 126. A regulating valve 136 connects pipe to pipe 124.A gauge 138 connected to pipe 124 indicates the air pressure within thesystem. Air pumped into the system by pump 126 passes through valve 136and through pipe 124 into cylinder 116 below piston 120. This air tendsto drive the piston 120 and the piston 122 upwardly as viewed in Figure2 to exert a pressure on the oil in cylinder 118. The oil, beingsubstantially incompressible, transmits this pressure to the pistons 24through the respective valve assemblies 32, 34-, 36 and 38. It is to benoted that the area of piston 120 on which the air under pressure actsis much greater than the area of piston 122 which acts on the oil incylinder 118. Owing to this difference in the area of the pistons, aparticular pressure per unit area applied to piston 120 results in amuch greater pressure per unit area exerted on the oil by piston 122.Stated otherwise, my accumulator 114 provides a multiplication ofpressure.

I- provide motor 132 with a regulating system which ensures-that thepressure exerted on piston 120 is within certain predetermined limits. Arod 140 carried by piston 120 for movement with it, passes through anopening 142 in the top of cylinder 116. Respective spaced fingers 144and 146 on the rod are adapted to actuate limit switch arms 148 and 150as piston 120 moves respectively down and up in cylinder 116. The limitswitches 152 and 154 associated with arms 148 and 150 control theoperation of motor 132. Respective conductors 156 and 158 connect motor132 to the terminals 160 and 162 of a suitable source of electricalenergy. Limit switch 154 has a normally closed contact arm 164 connectedin series with a normally-open contact arm 166 in conductor- 156; Withneither of the fingers 144 or 146 engaging an arm 148 or- 150, theswitches are in the. condition; shown in Figure 2 and motor 132'is notenergized; If 'the pressure under piston 120 dropsbelow apredeterhrinedpressure, finger 144 engages arm 148 to close the contact arm 166 ofswitch 152. This action completes the circuit of motor 132 which drivespump 126 to supply fluid under pressure to cylinder 114. As the pressureunder piston 120 increases, the pistonmoves upwardly and am 148 isreleased. In order to maintain the circuit .of motor 132 after arm 148is released, I connect a relay winding 168 between conductors 156 and158. When arm 166 is closed, winding 168 is energized to close anormally open switch 170 through a linkage 172. I connect switch 170across arm 166 to maintain the motor circuit after finger 144 releasesarm 148 to permit arm 166 to open. As pump 126 continues to drive airinto cylinder 114, piston 120 moves upwardly until finger 146 actuatesarm 150. When this occurs, switch arm 164 opens to interrupt the circuitof motor 132 and the circuit of holding relay 168.

The motor stops and its control circuit is returned to its initialcondition.

When any one of the valve assemblies 32, 34, 36, and 38 is actuated,fluid is permitted to pass .out of the system through relief pipes 46.It may pass from these pipes into any suitable means such as a sump tankor the like 174.

When an overload occurs owing to an irregular sheet of stock being fedto the press, it is desirable that the press be stopped. Referring toFigure 3, a plug 176 screwed into a bore in the wall of body 40 slidablysupports a switch actuating pin 180. A spring 182 bears between plug 176and a head 184 formed on pin 180. When piston 48 moves to the right asviewed in Figure 3, its head 52 cams pin 180 outwardly of bore 42against the action of spring 182. The resulting movement of pin 180 isemployed to actuate a suitable control (not shown) of a type known tothe art to stop the press by unclutching the press drive from theflywheel. It is to be understood that I provide a switch actuating pin180 for each of the valve assemblies 32, 34, 36, and 38.

Referring now to Figure 4, I have shown a second form of my overloadrelief assembly for a power press including a blank holder slide 182mounted for reciprocation on a press frame (not shown) in a manner knownto the art and an inner slide 184 also mounted for reciprocation on thepress frame within the blank holder slide. The press, which may forexample be a two-point suspension press, includes respective inner slidedrive pitmans 186 and 188 which are driven in a manner known to the artto reciprocate inner slide 184. Respective pins 190 and 192 carryingbushings 194 and 196 pivotally connect pitma'ns 186 and 188 to the heads198 and 200 of inner slide adjusting screws 202 and 204. Respectiveadjusting nuts'206 and 208 have threaded bores through which screws 202and 204 pass. Worms (not shown) are driven in a manner known to the artto drive nuts 206 and 208 to adjust the position of slide 184 on thepress frame.

, Slide 184 carries a pair of cylinders 210 and 212 which houserespective pistons 214 and 216. Respective passages 218 and 220 areadapted to admit fluid under pressure to the interior of cylinders 210and 212 to force pistons 214 and 216 upwardly as viewed in Figure 4against stop rings 222' and 224 carried by the cylinders. Bolts 226secure respective housings 228 and 230 disposed over nuts 206 and 208 tothe pistons 214 and 216.

I provide a hydraulic system, similar to that described in connectionwith thetie rod rr'eli'ef system shownin Figures 1 to 3, for supplyingfluid under pressure to cylinders 210 and 212. This system includesrespective valve assemblies indicated generally by the referencecharacters 232 and 234, the outlet ports of which are connected tocylinders 210 and 212. Valve assemblies 232 and 234 are of the sameconstruction as the valve assemblies 32, 34, 36, and 38 of the form ofmy invention shown in Figure 2. The remainder of the fluid system of theform of my invention shown in Figure 4 is the same as that of carried byinner slide 184 operates to supply fluid such as oil under apredetermined pressure to pipe 94. The inlet ports of the respectivevalves 232 and 234 are connected to pipe 94. Pump 96 which supplies oilto the accumulator 114 over the piston 122 has its intake 102 disposedin a reservoir 236 formed in or carried by the inner slide 184. Thesystem for supplying air under pressure to accumulator114 under piston120 is the same as that shown in Figure 2.

While in Figure 4 I have shown a two-point suspension press, it is to beunderstood that a four-point system may as well be used. Further, whileI have shown a relief sys tem for the press inner slide, it is to beunderstood that a similar system could be applied to the drivingconnections of blank holder slide 182. In any case, the operation of thesystem is the same.

In operation of the form of my improved overload relief assembly forpower presses shown in Figures 1 to 3, the motor drives pump 96 tosupply oil to the system. Motor 132 is driven to supply air to'cylinder114 under piston to exert a predetermined pressure on the oil in thesystem. The oil transmits this pressure to the respective pistons 24carried by the press tie rods. In the normal condition of my system thetie rods are thus placed under a predetermined tension. When any one ofthe rods is overloaded, its piston 24 displaces fluid out of thecylinder 30 and into the bore 42 of the associated valve assembly 32,34, 36, or 38. As a result of this action, the piston 48 moves to. theright as viewed in Figures 2 and 3 to permit communication betweenenlargements 60 and 74 to permit the oil in the system to flow out ofrelief pipes 64 into sump 174. I construct piston 48 so that the valveformed by the engagement of the piston wall with the part of the borebetween enlargements 60 and 74 opens slightly before head 52 is unseatedto. permit the system pressure to be relieved slightly be fore thepressure on the overloaded rod is relieved. When any one of the valveassemblies 32, 34, 36, or 38 is actuated', pressure throughout thesystem is relieved. Owing to the normal tension on the remaining tierods of the system, these rods force fluid out of their associated cylinders 30 against the relieved pressure in the supply system to actuatetheir respective valve assemblies. It will be seen that actuation of anyone of the valve assemblies results in operation of the remaining valveassemblies with the result that tension on all the tie rods is relieved.Motor 132 maintains the fluid pressure in the system through accumulator114 in a manner described hereinabove. Any oil lost during an overloadis replenished by the operation of pump 96.

In operation of the form of my invention shown in Figure 4, if the pressinner slide 184 encounters a load overa predetermined load so that oneof, or both of,

the pitmans-186 or 188 is overloaded, the system operates to. relievethe load on both pitmans. Assuming for example, that pitman 186 isoverloaded, its associated pis ton 214 forces fluid back through passage218 to valve assembly 232. In response to this fluid, the piston 48moves to the right as viewed in Figure 3 to permit fluid entering thevalve assembly to flow through ports 72 and from annular recess 74 torecess 60 and from recess 60 through relief pipe 64 back to thereservoir.

After this connection is established, piston head 52 moves a slightdistance to the right as viewed in Figure 3 to permit fluid. from thecylinder 210 to flow out through relief pipe 64' press tie. rods. inresponse to an overload imposedon any one of the rods. My systempreventsdamage to the press. parts owing to an unsymmetrical overloadapplied to the press as. when. a sheet or material of irregularthickness is. fed. to the press. My system operates in response to anoverload onany one of. the presstie rods. It may be applied to, press:slides suspensions as well as; to the. tie rods;

It; will be, understood that: certain features: and subcombinations areof utility and. may be employed without reference to other features;and, subcombinations. This is contemplated. by and is. within the scopeof. my claims. It is further obvious that. various. changes. may bemadein details Within the. scopeof my claims without departing from the.spirit, of my invention. It is therefore to be understood that; myinvention is notto, be limited to the specific details shown anddescribed,

Having thus described my invention, what. I claim, is:

1. In a power presshavinga pair of elements subjected to stress andamcmber to which said elements are connected, respective piston andcylinder units for connecting said elements to said member, said unitsbeing adaptedv to transmit stress between the respective elements andsaid member when fluid under pressure is present in the cylinders, acommon fluid systemfor supplying fiuid to said units, and respectivevalve assemblies providing communication between said cylinders and saidsystem, each of said assemblies comprising a valve responsive to apredetermined pressure difierence between the associated cylinderpressure and the common. system pressure resulting. froman increase incylinder pressure for relieving the common, system pressure.

2. In. a. power press having. a pair of elements subjectedto stress anda member to which said elements are connected, respective piston and.cylinder units for connecting said elements to said member, said unitsbeing adapted to transmit. stress between the respective elements andsaid member when fluid under pressure is present in the cylinders, 21common fiuid system for supplying fluid to said units, and. respectivevalve. assemblies providing communication between said cylinders andsaid system,

each of said valve assemblies comprising a first normally closed valveadapted to relieve the pressure in its corresponding cylinder and a.second normally closed valve.

adapted to relieve the, pressure in said system, each of. said first andsecond valves being responsiveto a predetermined increase in pressure inthe corresponding cylinder to relieve the system and cylinder pressure.

3. Apparatus as in claim 2 in which each of said assemblies. includes acheck valve for connecting said system to the corresponding cylinder.

4. Apparatus as in claim 2 in which said first and second valvescomprise a valve cylinder formed with a pair of respective valveseats, apiston disposed within said valve cylinder having a pair. of valve headsfor cooperation with the respective seats, a relief opening formed insaid valve cylinder between said seats, means normally urging saidpiston to seat said heads, said piston urging means being responsive toa. predetermined pressure to permit said piston to move to unseatsaidheads.

5. Apparatus as in claim 2 in which said first and second valvescomprise avalve cylinder for-med with a pair of respective spaced valveseats, ahollow piston disposed within said valve cylinder and having apair of valve heads for cooperation. with the. respective seats, means.

providing communication between said system and one end of; saidvalvecylinder, means providing communica tionbetween. theother end; of: thevalve cylinder and the. corresponding; unit cylinder, means. forming arelief opening in said valveicyli'nd'er between said valve seats, andmeans for urging said piston to seat said. heads on said seatsto.prevent communication-between said system and said relief openingand. between said corresponding unit cylinder and said relief opening,said: piston urging means being responsiveto a predetermined increase inpressure in. said corresponding-unit cylinder to permit said piston tobe displaced torelieve-the pressure in said unit cylinder and in saidsystem.

i 6. Apparatus as in claim 2 in which said first and secand valvescomprise a valve cylinder formed with a pair ofrespectivespacedvalveseats, a hollow piston disposed within said valve cylinder andhaving a pair of valve heads for cooperation with the respective seats,means providing communication between said system and one end of saidvalve cylinder, means providing communication between the other end ofthe valve cylinder and the corresponding unit cylinder, means forming arelief opening in said; valve cylinder between said valve seats, meansfor urging said piston to seat said heads on said seats to preventcommunication between said system and said relief opening and betweensaid corresponding unit cylinder and said'reliefopening, said-pistonurging means being responsive-to a predetermined increase in pressurein, said corresponding-unit cylinder to permit said piston to bedisplaced. to-relievethe pressure in said unit cylinder and in saidsystem, and a check valve bypassing said first and second valves toconnect said unit cylinder to said source.

7. Apparatus as inclaim 2 in which said common fluid systemcomprises anaccumulator having a first cylinder and a second cylinder, said firstcylinder having a small diameter relative to the diameter of the secondcylinder, respective'first and second pistons disposed in saidcylinders, means connectingsaid first and second cylinders for movementas a unit, means for supplying air under pressure to said secondcylinder and means responsive to. movement of said pistons forregulating said air supplying means.

8. Apparatus as in claim 2 including means for causing said second valveto operate slightly in advance of. said first valve in response to saidpredetermined pressure increase in the corresponding cylinder wherebysaid' system pressure is relieved slightly before said unit pressure isrelieved.

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